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This chapter focuses on the climates of Uranus, Neptune, and exoplanets. Uranus spins on its side, which allows a comparison between sunlight and rotation for their effects on weather patterns. In contrast to Venus, Uranus is only weakly affcted by tides from the Sun because it is so far away. Models of planet accretion give a gradual clumping of small bodies into medium-sized bodies and then into large bodies, until finally only a few large bodies are left. The final collisions, which involved these large bodies, would have been quite violent and were capable of knocking Uranus on its side. After providing an overview of Uranus's rotation, insensitivity to seasonal cycles, and wind profile, the chapter considers Neptune's winds, effective radiating temperature, and Great Dark Spot. It also explains the radial velocity method and the transit method of detecting extrasolar planets.

This chapter traces the critical history that has given rise to the notion that Milton’s epic universe accords with the Ptolemaic system. Almost every editor since Newton (1749) has presented us with a geocentric universe, and many modern editors equip that universe with solid spheres, usually with holes in the top to facilitate travel between heaven and earth. Milton’s own text gives very little warrant to this picture: just three lines in a satirical context. Early critics recognized that these lines were a joke and that Milton consigns Ptolemaic spheres to the Paradise of Fools. Early critics also recognized that the shell of Milton’s universe is not the Ptolemaic primum mobile, but a shield against Chaos that Milton took from Lucretius. This chapter argues that the early critics are right and tries to show exactly how and when the critical perception of Milton’s universe went wrong.

Sara Seager, the pioneering astrophysicist, mathematician and planetary scientist reflects in this dialogue about how exoplanets, the purpose of her science, discovered her before she discovered them. She also explains her relationship with mathematics and why for her physics is the most beautiful way to describe the universe, as well as explaining the growing scientific interest to discover planets that orbit a star different to our sun. Later, Sara explains that all astrophysics projects she works on are very long term and is consequently concerned about whether there will be enough young people in this world of immediacy with sufficient patience to become astronomers. She also goes on to explain why life capable of travelling across galaxies will be non biological, as well as discussing how, and with what help, she is facing the greatest challenge of her life: trying to find another Earth, in other words, another planet like Earth with signs of life.

Many exoplanets have been discovered in recent years by searching for regular dips in brightness of a star as a planet passes across its face. NASA’s Kepler Space Telescope was launched to search for exoplanets using this planetary transit method. Kepler monitors 145,000 stars and has so far discovered over 2500 exoplanets. The planetary transit method has also been used to find a family of seven planets around a nearby red dwarf star that has been named TRAPPIST-1.

Frank Drake devised the Drake equation to estimate the number of advanced civilizations in the galaxy with the aim of gathering support for SETI (the Search for Extraterrestrial Intelligence). The earliest attempts to detect radio signals from extraterrestrials date back to the 1960s. Paul Allen has funded the Allen Telescope, Array which is dedicated to searching for such signals. When complete it will include 350 radio dishes. The citizen science project SETI@Home allows anyone with a home PC to participate in analysing the data amassed by the SETI project.

At the Dwight D. Eisenhower Presidential Library, an archivist named Herb Pankratz specializes in queries about the thirtyfourth president’s exopolitics. Pankratz assumed this responsibility because of his expertise in transportation. Since exopolitics involves diplomacy with visitors from other planets, his colleagues deemed him the best qualified person on staff to field questions, of which there are many, since Ike is alleged to be the first president to have negotiated directly with aliens. Neither Pankratz nor anyone else at the Dwight D. Eisenhower Presidential Library is able to confirm these historic events. They tell researchers that the president’s presumed first meeting with extraterrestrials, on the evening of February 20, 1954, was in fact a dental appointment. They inform people that Eisenhower’s emergency departure from the Smoking Tree Ranch, where he was vacationing, was on account of a chipped porcelain cap on his upper right incisor, broken when he bit down on a chicken bone, not a secret meeting at Edwards Air Force Base with aliens requesting that he end America’s nuclear weapons program in order to protect the space-time continuum. The archivists have no record of the words with which Ike rebuffed his celestial guests without causing an intergalactic diplomatic rift, nor of the accord he allegedly reached with a different alien race later that year, allowing them to borrow cows and humans for purposes of medical examination, provided that they return the specimens unharmed. The lack of documentation has not been taken as want of evidence by organizations such as the Exopolitics Institute. On the contrary the information gap has only further convinced them of a governmental cover-up, extending to the present day, a “truth embargo” involving not only Secretary of State Hillary Clinton but also the United Nations. As a conspiracy theory exopolitics is barely worthy of a B movie. Even without asking how these extraterrestrial ambassadors have avoided public exposure for over half a century, one might legitimately wonder why the world’s governments have so persistently hidden them, and why beings of allegedly superior intelligence have proven so complacent.

This chapter highlights the amazing diversity of exoplanet worlds: planets can orbit neutron stars and giant stars, evaporate in the heat of their stars or have deep oceans, and may suffer from everlasting daysides and nightsides. A few enjoy two or more suns, and some bear a rough similarity to Earth with possible liquid water on their surface. The author describes how exoplanets reveal themselves through signatures in the light of their stars. The first exoplanets were found in unexpected places, but after determining where exoplanets could or could not be spotted with current detection methods, intrinsic statistical properties emerged. Some are in line with the Solar System, but many are not. What is clear is that exoplanets are more numerous than the stars in our Galaxy.

The landscapes of exoplanets are likely to be incredibly diverse: exoplanets come in a large range of sizes and masses, and therefore surface gravities. Atmospheres can be thick layers, or absent. The interior makeup of exoplanets is even harder to know, but the formation scenarios of the giant planets and the remains of planets found in white-dwarf atmospheres provide insights. All that knowledge, combined with information on the central stars and other exoplanets within a system, provides a view of past, present, and future environments. This chapter reviews sample exoplanets and the conditions on their surfaces.

The author takes us to visit Saturn’s moon Titan, and Venus, Mars, and to the unconfirmed planet GJ581d. Although we find unearthly conditions on these bodies’ surfaces today, things were different in the past. Even now, there are oceans deep below Titan’s frozen ice shell that itself sees liquid methane rains and vast ethane-filled lakes. Venus and Mars both had liquid water long ago, while Venus may even have been comfortably warm and humid before modern complex life developed on Earth. Many potentially habitable exoplanets are likely locked in their rotation to always face their star with the same side, causing incredible differences between their day and night sides. This chapter reviews how oceans and atmospheres are lost by the Sun’s magnetism or protected by that of the planets’, how masses of carbon dioxide can be stored in solid limestone, and how habitable zones shift to and from planets.

How many planetary systems formed before our’s did, and how many will form after? How old is the average exoplanet in the Galaxy? When did the earliest planets start forming? How different are the ages of terrestrial and giant planets? And, ultimately, what will the fate be of our Solar System, of the Milky Way Galaxy, and of the Universe around us? We cannot know the fate of individual exoplanets with great certainty, but based on population statistics this chapter sketches the past, present, and future of exoworlds and of our Earth in general terms.